“Human beings by their very nature make mistakes; therefore, it is unreasonable to expect error-free

human performance.” (Shappell & Wiegmann, 1997)

• It is not surprising then, that human error has been implicated in 60-90% of all accidents.

• However, the rate of human error accidents has remained relatively stable over the past 20 years, whereas accidents associated with mechanical failures have been virtually eliminated.

• … is an inappropriate or undesirable human decision orbehavior that reduces or has the potential for reducing theeffectiveness, safety, system performance (Wickens, 2002).

• A human action/decision that exceeds system tolerances.

• An action is taken that was not intended by the actor; notdesired by a set of rules or an external observer; or that led thetask or system outside its acceptable limits (Senders & Moray,1991).

5

• Recklessness

• Stubbornness

• Nervousness

• Slowness to learn

• Fatigue

• Stress

• Psychologies

• 1st blame only the individual

• 2nd identify other factors. Eg :

• badly designed or faulty equipment

• poor management practices

• inaccurate or incomplete procedures

• inadequate or inappropriate training

• Operator error :

• Due entirely to the human operator.

• You can’t eliminate all of these, but a good human factors design will make these virtually impossible.

• Design error

• Due to poor design.

What’s wrong with these designs? (Left to right : stove, door, refrigerator)

• Omission - forget/failure to do something

• Commission - doing the task incorrectly

• Sequence errors - task or set of task performed in the wrong sequence out of order

• Timing errors - person fails to perform the action within the time allotted too slow - too fast - too late

• Intrusion – entering a dangerous area / location

• Reversal – trying to stop or undo a task already initiated

Basic Errors

Unsafe Acts

Unintended Action

Intended Action

Slip(Skill-based)

Lapse(Skill-based)

Mistake

Violation

Attentional Failures

Memory Failures

Rule-based orKnowledge-based

Mistakes

Routine violationsExceptional violations

Sabotage

• Slips and Lapses

• Slips and lapses occur in very familiar tasks which we cancarry out without much conscious attention, eg driving avehicle. These tasks are very vulnerable to slips and lapseswhen our attention is diverted even for a moment.

• Slips

• (‘Whoops’) Not doing what you’re meant to do.

• Lapses

• Forgetting to do something, or losing your place midwaythrough a task.

• Slips and lapses occur when:• the task is very familiar and requires

little thought;• people confuse two similar tasks;• tasks are too complicated and long-

winded;• the main part is done but the finer

details are missed;• steps in a procedure don’t follow

naturally; and• there are distractions and

interruptions.

• How to reduce slips and lapses:• make all workers aware that slips and

lapses do happen;• use checklists to help confirm that all

actions have been completed;• include in your procedures the setting

out of equipment, site layout and methods of work to ensure there is a logical sequence;

• make sure checks are in place for complicated tasks; and

• try to ensure distractions and interruptions are minimized, eg mobile phone policy.

Remember, simply adding more training will not eliminate slips and lapses. Effective procedures are required. Ask yourself: ‘How can I make sure my workers understand that they are vulnerable to slips and lapses?’

• Mistakes are decision-making failures. The two main types ofmistake are rule-based mistakes and knowledge-basedmistakes. They arise when we do the wrong thing, believing it tobe right.

• Examples of mistakes include :• making a poor judgment when overtaking, leaving insufficient room to

complete the maneuver in the face of oncoming traffic; and• an operator misinterpreting the sound of a machine breakdown and

failing to switch off immediately.• Why do mistakes occur?

• Doing too many things at the same time.• Doing too many complex tasks at once.• Time pressures.

• Factors which contribute to people making mistakes• The work environment – eg too hot, too

cold, poor lighting, restricted workspace, noise.

• Extreme task demands – eg high workloads, boring and repetitive jobs

• Social issues – eg conflicting attitudes of workers on how to complete work

• Individual stressors – eg drugs and alcohol, lack of sleep, family problems, ill health.

• Equipment problems – eg inaccurate or confusing instructions and procedures.

• Organizational issues – eg failing to understand where mistakes can occur and implement controls,

• How you can reduce mistakes• To avoid rule-based mistakes,

increase worker situational awareness of high-risk tasks on site and provide procedures for predictable non-routine, high-risk tasks.

• To avoid knowledge-based mistakes, ensure proper supervision for inexperienced workers and provide job aids and diagrams to explain procedures.

Ask yourself: ‘How can I reduce the likelihood of mistakes occurring on this site?’

• The goal of human reliability analyses is to apply the same principles tothe human operator that we apply to the machine/device to prevent errorthat leads to system failure.

• Human Error Probability - the ratio of errors made with respect to thenumber of opportunities for error;

• P (error) = 1 - Human Reliability

• Human reliability = 1 - operator error probability.

Technique for human error rate prediction (THERP)

Hazard and operability study (HAZOP)

Skill, rule and knowledge model (SKR)

Systematic human error reduction and prediction approach(SHERPA)

Generic error modeling system (GEMS)

Potential Human Error Cause Analysis (PHECA)

Murphy Diagrams

Critical Action and Decision Approach (CADA)

Human Reliability Management System (HRMS)

Influence modeling and assessment system (IMAS)

Confusion Matrices

Cognitive Environment Simulation (CES)

• A key objective of HF is to reduce accidents and improve safety

• INCIDENT - An incident is an unplanned, undesired event thatadversely affects completion of a task.

• ACCIDENT - An undesired event that results in personal injury orproperty damage.

• NEAR MISS - Near misses describe incidents where no propertywas damaged and no personal injury sustained, but where, given aslight shift in time or position, damage and/or injury easily couldhave occurred.

1. Management (organization/policies)

2. Environment (physical conditions)

3. Equipment (design)

4. Work (task characteristics)

5. Social/psychological environment (culture)

6. Worker/coworkers (personal attributes)

• A person's social environment (the worker's family or life )Social Environment /

Ancestry

• Undesirable personality traits, such as stubbornness, greed, and recklessnessFault of person

• The central factor in preventing incidents, and the easiest causation factor to remedy. Caused by improper attitude, lack of knowledge or skill, physical unsuitability, or improper mechanical or physical environment.

Unsafe Act / Conditions

• Events, such as falls of persons, striking of persons by flying objects are typical accidents, that cause injuryAccident

• Injury results from accidentsInjury

Accident & Injury

Latent Conditions

Latent Conditions

Latent Conditions

Active Conditions

Failed orAbsent Defenses

OrganizationalInfluences

UnsafeSupervision

Preconditionsfor

Unsafe Acts

UnsafeActs

Swiss-Cheese Model(Systems have multiple layers of

defense, but all of them have holes)

• Fail to perceive hazard

• Underestimated hazard

• Fail to respond to recognized hazard

• Respond to hazard, but ineffectively

• Apply human factor principles to design

• Provide procedural checklists

• Provide training

• Provide appropriate & meaningful feedback

• Incentive programs

• Eliminate/reduce risk through design